Secretion of met-enkephalin-like peptides and catecholamines from adrenal glands into the circulation was studied in dogs with indwelling cannule in the lumbar adrenal vein. Splanchnic nerve stimulation increases the simultaneous release of met-enkephalin-like peptides and catecholamines, a response which was mimicked by nicotinic receptor agonists and blocked by hexamethonium. The content of met-enkephalin-like peptides was similar in control and reserpine-treated dogs, while the catecholamine content was reduced. Splanchnic nerve stimulation in reserpinized dogs increased the release of met-enkephalin-like peptides into the lumbar and renal vein, that was associated with a naloxone-reversible decrease in arterial blood pressure.